1. Area of the Art
The present invention relates to determining the presence of occult blood in fecal matter, and more particularly to a system for reading and interpreting guaiac-based occult blood tests.
2. Description of the Prior Art
Each year, more than 130,000 Americans are diagnosed with colorectal cancer. Of those afflicted, an estimated 56,000 die—a death toll that ranks this cancer as the second highest, for women and men, among all types of cancers. Scientific evidence suggests that the majority of colon cancers arise from the evolution of normal mucosa progressing into adenomas and finally to adenocarcinomas. Adenoma removal correlates with a reduced risk of rectal carcinomas; analogously, the removal of adenomatous polyps, reduces the likelihood of colon cancer (U.S. Pat. No. 5,790,761). Unlike other forms of cancer, early diagnosis and treatment of colorectal cancer results in a high cure rate of more than 90%. If, however, the disease is not detected until the later stages, the cure rate drops drastically to 25% or less (U.S. Pat. No. 5,264,181). Thus, early detection of the disease is critical to successful treatment of colorectal cancer.
Occult (hidden) blood in feces is an early sign of colorectal cancer, adenomas and polyps. It is undetectable to the naked eye, because the blood is present in minute amounts. Tests and procedures for detecting occult blood in fecal matter are well-known. One of the most successful tests is offered by Beckman Coulter, Inc. (Fullerton, Calif.) under the trademark HEMOCCULT® and disclosed in U.S. Pat. No. 3,996,006 issued to J. F. Pagano. Briefly, a thin smear of fecal matter is applied to one side of the guaiac paper. Then, a developing solution, such as hydrogen peroxide, is applied to the opposite side of the guaiac paper. If blood is present in the fecal matter, the guaiac reaction will color the paper blue. Recently, a similar but more sensitive test has been introduced under trademark HEMOCCULT® SENSA® by Beckman Coulter, Inc.
Guaiac-based tests are rapid, simple, disposable, and convenient for use in doctors' offices, hospitals and other point-of-care locations for the quick diagnosis of conditions associated with colorectal cancer. However, since these tests are visually-read and the results are recorded manually, the conventional guaiac test formats are not suitable for use in high volume settings required by many diagnostic laboratories.
Another problem associated with these guaiac tests is instability of the test results. Test paper must be examined within 60 seconds after the addition of the developer to prevent inaccurate interpretation of the test results due to color fading. Additionally, some conventional guaiac tests suffer from insufficient sensitivity, which leads to a relatively high number of negative test results in fecal samples from known bleeding patients.
Finally, in certain applications, semiquantitative data may have greater value than qualitative results. Conventional visual reading methods of guaiac test interpretation, however, provide only qualitative results.
In view of the deficiencies of the related art, there is a need for an accurate and highly sensitive device for automated or semi-automated interpretation of fecal occult blood tests (FOBTs). There is also a need for novel, highly sensitive, and semiquantitative analysis methods for use in occult blood testing.